Epigenetics, phenotypic plasticity and the evolution of adaptive responses

Abstract

In the fourth lecture, the role of epigenetics in phenotypic plasticity and the evolution of adaptive responses was discussed. The question of whether acquired traits can be inherited from one generation to the next was first posed by Lamarck. We now understand that an organism's capacity for phenotypic plasticity is based on DNA sequence and is itself an adaptive trait. In some environments, when a " acquired "trait(a form of a trait that exhibits phenotypic plasticity) becomes permanent, this appears to be due to mutations that have " fixed " the plastic trait (genetic assimilation). Mary Jane West-Eberhard postulated in 2003, based on research on wasps and butterflies, that phenotypic plasticity could pave the way for permanent adjustments in an organism that has to survive in variable environmental contexts. She proposed that some of these genetic changes would simply increase the proportion of the most flexible individuals, while others might favor a specific trait. Lamarck was undoubtedly right to point out that rapid, flexible responses to the environment can lead to lasting changes. However, most lasting changes seem to be due to mutations in the DNA sequence that fix them. The mutations underlying phenotypic plasticity are undoubtedly considerable drivers of evolution, given the importance of adaptation to changing environments. As Darwin wrote :" It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that best adapts to change. "

Nevertheless - and given the role of epigenetic factors in the flexible responses of certain organisms such as bees or plants - a recurring question concerns the place of epigenetic processes not only in the response to environmental change, but also in the adaptation of species, for example to climate change, in various ecosystems.

It is now clear that epigenetic processes are likely to be involved in adaptive responses, across the whole spectrum of life. Epigenetic processes are involved in perpetuating environmentally-triggered differential gene expression profiles, but these are based on a genetically-defined potential. If we refer to P. Medawar's well-known expression :" genetics supposes, epigenetics disposes ", the role of epigenetics in adaptive mutations and in the acceleration of evolution nevertheless remains a fascinating question. This topic was addressed in my 2017 lectures in the context of the epigenetic control of transposable elements, which can have significant mutagenic potential, particularly under conditions of environmental stress.